QuestionI have a Briggs twin cylinder 18.5 hp, model 42a707, it starts and runs good, until you start to use the mower (Murray GT) after you have had it in gear and moving for about 2-3 minutes, it starts losing power, if you put it at about half choke, it recovers most of its power, but engage the blades and it loses its power again, even with it in half choke. I've rebuilt the carb, which helped its idling a lot, but did nothing for the power. Could the jets be out of adjustment, I snugged them and then backed both out 2 and 1/2 turns. It has the carb with three screws holding the pump on. I've also put in new plugs, checked coil, drained and flushed out gas tank. Thank you for any help you can give me.
AnswerSam,
It sounds like one cylinder is not running. There are two simple test to confirm this, one is a compression test. Simply remove both spark plugs and insert a compression gauge (one cylinder at a time) and see if you have readings in both cylinders.
Another simple test is to remove ONE spark plug wire at a time and start your engine. Does it run on one cylinder, but not the other? WALA! Cylinder problem!
The most common problem I see with this engine is that mice sometimes build a nest above the cylinder in the cooling fins over the winter, the engine is started in spring-overheats and the exhaust valve seat pops out of the casting. This is not repairable...Replacement engine is needed.
If you have a cylinder problem, be very cautious sticking money into the engine as some parts for this engine are no longer available.
Hope this helps...drop me a followup and let me know what you find!
